Sierra Ladrones Formation

Sierra Ladrones Formation
Stratigraphic range: Pleistocene to Pliocene 5–2  Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Sierra Ladrones Formation northeast of Socorro, New Mexico, USA
Type	Formation
Unit of	Santa Fe Group
Overlies	Popotosa Formation
Thickness	470 m (1,540 ft)
Lithology
Primary	Sandstone
Other	Siltstone, conglomerate
Location
Coordinates	34°23′38″N107°00′03″W / 34.3939496°N 107.0007996°W / 34.3939496; -107.0007996
Region	New Mexico
Country	United States
Type section
Named for	Sierra Ladrones (mountain range)
Named by	M.N. Machette
Year defined	1978;47 years ago (1978)
Sierra Ladrones Formation (the United States) Show map of the United States Sierra Ladrones Formation (New Mexico) Show map of New Mexico

The Sierra Ladrones Formation is a geologic formation exposed near the Rio Grande Valley in New Mexico. It preserves fossils of Pliocene to Pleistocene age. ^[1]

Description

The formation consists of three facies representing different depositional environments. These are piedmont slope and alluvial fan deposits, typically composed of light-brown to light-reddish-brown sandstone and fanglomerate; axial stream deposits, which are composed of light-gray to light-yellowish-brown fine- to medium-grained sand and sandstone with fluvial cross-bedding and cut-and-fill channels; and interbedded basalt flows with a K-Ar age of 4.5 +/-0.1 million years (Ma. The total thickness is in excess of 470 m (1,540 ft). ^[1] The formation unconformably overlies or is in fault contact with the Popotosa Formation or older formations. Its age is early Pliocene to middle Pleistocene (2 Ma to 5 Ma.) ^[1]

The formation is interpreted as fanglomerates shed from the flanking uplifts of the Rio Grande Rift and channel and floodplain deposits of the ancestral Rio Grande. ^[2]

Fossils

The formation has yielded abundant fossils of Irvingtonian age at Tijeras Arroyo, south of Albuquerque International Airport. These include Hypolagus , Equus , Mammuthus , and Hesperotestudo . ^[3]

History of investigation

The formation was defined by M.N. Machette in 1978 for exposures in the Sierra Ladrones, a range of low foothills of the Ladron Mountains, in the Sevilleta National Wildlife Refuge. ^[1]

The formation was subsequently mapped into the lower Rio Puerco valley ^[4] and as far north as the Santo Domingo basin. ^[5]

Footnotes

1. Machette 1978.
2. Osburn & Chapin 1983.
3. Lucas 1997, p. 228.
4. Love & Young 1983, p. 280.
5. Smith & Kuhle 1998.

See also

• Earth sciences portal
• Paleontology portal

• List of fossiliferous stratigraphic units in New Mexico
• Paleontology in New Mexico

References

• Love, David W.; Young, John D. (1983). "Progress report on the late Cenozoic geologic evolution of the lower Rio Puerco" (PDF). New Mexico Geological Society Field Conference Series. 34: 277–294. Retrieved 18 May 2020.
• Lucas, Spencer G. (1997). "New Mexico's Fossil Record 2". New Mexico Museum of Natural History and Science Bulletin. 16. Retrieved 18 May 2020.
• Machette, M.N. (1978). "Geologic map of the San Acacia quadrangle, Socorro County, New Mexico". U.S. Geological Survey Geologic Quadrangle Map Series. GQ-1415. Retrieved 18 May 2020.
• Osburn, G.R.; Chapin, C.E. (1983). "Nomenclature for Cenozoic rocks of northeast Mogollon-Datil volcanic field, New Mexico". New Mexico Bureau of Mines and Mineral Resources Stratigraphic Chart Series. 1. Retrieved 18 May 2020.
• Smith, G.A.; Kuhle, A.J. (1998). "Geology of the Santo Domingo Pueblo and Santo Domingo Pueblo SW 7.5-minute quadrangles, Sandoval County, New Mexico". New Mexico Bureau of Mines and Mineral Resources Open-File Map Series. OF-GM 15/26. Retrieved 18 May 2020.